Suunto Balancing Zones

[Venio]

I know that Suunto balances their compasses in 5 different zones. However, when I tried to find a marking on my SK-5 there was none. I assume since it is bought in the US it must me Zone 1. Does anyone know how to find the zone for sure?

[cummings66]

That's an interesting question and I'm curious how it works. I know our declination varies a LOT depending on what part of the country you live in, as a pilot all of our charts show that data.

I know I've heard that in the US you can only buy the version meant for here and if you take it abroad it might not be too accurate. I know that can be true.

If you're wondering if it's usable here I'd suggest a quick test. Get a good brand name compass and compare the two of them and see how it comes out.

If there's a serial number I'd say that's how you tell, most manufacturers denote special countries of origin that way.

[Krakenn]

This is a bit of a worry lads.

Are you serious? _ I mean 99.999% of the time who cares but ?

Kraks

[ScubaToys Larry]

The compasses don't change for declination, they change for inclination. The way to see is put it on a flat level table, and see if the compass rose sits flat. If you take a northern hemisphere one to the south, it will just have a tilt to it, so you would have to hold the compass at a slight angle so as not to have the rose hit the glass. Really, not that big of a deal.

And true, depending where in the US you are diving, you might be 6 or so degrees off from true north - but it's not like you are flying from california to vermont. You are swimming a few hundred yards - so if you're off by a few yards... no big deal. And when people give you directions to stuff.. they are going to give you compass headings - so their numbers will be off too. Stuff like, "From our dock, take a heading of 300 degrees and swim 200 yards and you should find the sunken treasure." I wouldn't bother ask, "Is that with or without compensating for declination?"... Unless of course it was a very large treasure!

[ScaredSilly]

Depending on the water vis (and treasure) I think I would ask for the declination. A 6 degree declination will result in a 10% (sin 6) error which over 200 yards will result in a 60 foot deviance. In 40 foot viz that may mean no booty. In places like the Pacific North West and North East it is up to 20 degrees which will put you at almost 35% off.

[ScubaToys Larry]

Originally Posted by ScaredSilly

Depending on the water vis (and treasure) I think I would ask for the declination. A 6 degree declination will result in a 10% (sin 6) error which over 200 yards will result in a 60 foot deviance. In 40 foot viz that may mean no booty. In places like the Pacific North West and North East it is up to 20 degrees which will put you at almost 35% off.

Yea, but the deal is, everyone else is dealing with the exact same thing. So you and your buddy say you are going to take a heading of 220, what does it really matter if in actuality it is 245? And to correct it, you would need a different compass anytime you went a few hundred miles in any direction. Now as soon as they have a DG for divers... that would be cool!

[ScaredSilly]

Originally Posted by ScubaToys Larry

Yea, but the deal is, everyone else is dealing with the exact same thing. So you and your buddy say you are going to take a heading of 220, what does it really matter if in actuality it is 245?

In that case you are correct. I agree who cares. I was thinking in terms actually locating something like a wreck (or treasure). Now a days with so many things being located with GPS you have to be able to correct.

Like the guy who lost his anchors and comes in a says I'll pay you $100 to go find it. Here are the GPS lat long coordinates.

Originally Posted by ScubaToys Larry

And to correct it, you would need a different compass anytime you went a few hundred miles in any direction.

Huh, people have been correcting for the declination for a long time with a regular compass. You just need to know the local declination and adjust acordingly by adding or subtracting from the true north reading. Map & Compass 101

[Venio]

Originally Posted by ScaredSilly

Huh, people have been correcting for the declination for a long time with a regular compass. You just need to know the local declination and adjust acordingly by adding or subtracting from the true north reading. Map & Compass 101

Which bring back the original question about knowing for what zone the compass was balanced in first place.

Now if someone points me to an underwater GPS unit, it will be mucho appreciated!

[Krakenn]

Just dont get lost and dont do the Advanced Diver Course in the Southern Hemisphere!

Smiles

Kraks

[tedtim]

Originally Posted by ScaredSilly

Depending on the water vis (and treasure) I think I would ask for the declination. A 6 degree declination will result in a 10% (sin 6) error which over 200 yards will result in a 60 foot deviance. In 40 foot viz that may mean no booty. In places like the Pacific North West and North East it is up to 20 degrees which will put you at almost 35% off.

You must first have a good understanding of the units you are using. There is a difference between true north, magnetic north, and grid north. If you know which one you are using, then you can make the appropriate correction. I have not seen an underwater compass that allows you to make a correction; they all point to true north.

Other factors come into play over which you may have no control. For instance, if there is a large iron deposit near you underwater, it can cause your compass to have an error.

As for a 60 foot error.... unless you are in water that has absolutely no current, you can read your compass to a one degree tolerance, you have exceptional skills to maintain a heading to within a one degree tolerance, and you have full confidence in the accuracy of the GPS readings (which have an error in most basic systems), you will have track error.

You do have to adjust your heading for the effect of current, but by how much depends on the speed of the current.

This almost sounds like - measure with micrometer, mark with chalk, cut with an axe.